This invention relates to a heatable appliance for personal use, in particular a hair-care appliance, including a device for the flameless combustion of a fuel/air mixture and an associated activation device for initiating its flameless combustion.
An appliance of this type is already known, for example, from U.S. Pat. No. 4,361,133. The device for flameless combustion is comprised of catalytically coated quartz wool which, for reasons of mechanical stability and a sufficiently accurate locating ability, is arranged between two spiral springs serving a supporting function for the quartz wool. The catalytically effective quartz wool serves for the flameless combustion of a fuel/air mixture supplied, the combustion heat being utilized for heating an appliance for personal use as, for example, for heating a gas-powered curling iron. However, the catalytic combustion action of the fuel/air mixture does not start until the catalytically active material has reached a specific activation temperature (LOT=light-off temperature). The energy required to obtain the activation temperature of the catalyst is supplied to the catalyst by means of an associated activation device. This activation device ignites a fuel/air mixture fed to a combustion chamber of the appliance after the fuel supply is started, the ignition being accomplished by means of one or several sparks or a flame introduced from outside, with the ignited fuel/air mixture becoming extinguished automatically within a fraction of one or several seconds. The energy released by this ignition is, however, sufficient to heat at least isolated zones of the catalyst to the activation temperature and to set off the catalytic, that is, the flameless combustion within the catalyst.
Whilst this appliance, sold in quantities in the million range in the past years, is well-established in practice, experience has shown that in single aspects the device for flameless combustion is still capable of improvement. First, the mechanical instability of the quartz wool and the resultant need to locate it in position by means of a mechanically stable supporting structure have given rise to problems. In the use of an appliance equipped with a catalyst of the type referred to above, it may happen that isolated fibers of the quartz wool fall out of their mechanical supporting structure which may adversely affect the passage of fuel by causing (partial) clogging of the fuel metering nozzle. Furthermore, loss of fiber may result in a deterioration of the activation action of the appliance, in particular where a piezoelectric igniter is used. Finally, the quartz wool is not in a position to ensure a consistent flow resistance at all times, so that hot spots may occur in partial areas of the catalyst. This impairs the service life of the catalyst materially.
On the other hand, it is precisely in the use of the known catalyst in hair-care appliances that the following problems occur: Specific user groups of such hair-care appliances heated by flameless combustion tend to apply hair-care products such as setting foams, hair spray, shampoo or the like prior to or while treating their hair. As a result, the air around the hair-care appliance is enriched with these hair-care substances or portions thereof to a greater or lesser degree. Some of this ambient air is aspirated by the fuel-heated hair-care appliance for producing a suitable fuel/air mixture. As comprehensive examinations have revealed, these hair-care products involve great disadvantages in respect of the useful life of the catalyst, particularly if they contain silicone-containing substances. If air enriched with hair-care agent is supplied to the catalyst for flameless combustion of the fuel, the tests performed and described in greater detail in the following reveal that a deposit of as little as 5 grams of hair-care agent accumulating on the catalyst is already sufficient to deteriorate the properties of the catalyst to a degree reducing the activation ability to intolerable values or to cause the degree of catalytic conversion of the fuel/air mixture to drop below a lower threshold. Therefore, appliances in which a deposit of more than 5 grams of hair-care agent accumulates on the catalyst are, as a rule, no longer usable, presenting a case for customer service.